Color-plus-clear composite coatings are widely utilized in the coatings art. They are particularly desirable where exceptional gloss, depth of color, distinctness of image, or special metallic effects are desired. The automotive industry has made extensive use of color-plus-clear composite coatings for automotive body panels. Such coatings, however, require an extremely high degree of clarity in the clearcoat to achieve the desired visual effect. As such, the clearcoat of a color-plus-clear composite coating is especially susceptible to a phenomenon known as environmental etch. Environmental etch manifests itself as spots or marks on or in the clear finish of the coating that often cannot be rubbed out.
It is often difficult to predict the degree of resistance to environmental etch that a clearcoat will exhibit. Many coating compositions known for their durability and/or weatherability when used in exterior paints, such as high-solids enamels, do not provide the desired level of resistance to environmental etch when used as the clearcoat of a color-plus-clear composite coating.
Many compositions have been proposed for use as the clearcoat of a color-plus-clear composite coating, such as polyurethanes, acid-epoxy systems and the like. However, many prior art systems suffer from disadvantages such as coatability problems, compatibility problems with the pigmented basecoat, solubility problems. Moreover, very few one-pack coating compositions have been found that provide satisfactory resistance to environmental etch, especially in the demanding environment of automotive coatings. Thus, there exists a continuing need for curable coating compositions that provide satisfactory resistance to environmental etch when used as the clearcoat of a color-plus-clear composite coating.